Synthesis of SAPO-44

ABSTRACT

A method for making molecular sieves comprising silicoaluminophosphate 44 (SAPO-44) or substantially pure SAPO-44 and a method for using the molecular sieves so prepared for oxygenate conversion to olefins.

This is a divisional of U.S. application Ser. No. 08/949,802, filed Oct.14, 1997, now U.S. Pat. No. 6,162,415.

FIELD OF THE INVENTION

The present invention relates to a method of synthesizing a molecularsieve comprising silicoaluminophosphate 44 (SAPO-44).

BACKGROUND OF THE INVENTION

Light olefins (defined herein as ethylene, propylene, butenes andmixtures thereof) serve as feeds for the production of numerouschemicals and polymers. Light olefins traditionally are produced bypetroleum cracking. Due to the escalating cost of crude petroleum, thereare increasing efforts to develop light olefin production technologiesbased on alternative feedstocks. An important type of alternativefeedstocks are oxygenates, such as alcohols, particularly methanol,dimethyl ether, dimethyl carbonate and ethanol. Alcohols may be producedby fermentation, or from synthesis gas derived from natural gas,petroleum liquids, carbonaceous materials, including coal, recycledplastics, municipal wastes, or any organic material. Because of the widevariety of sources, alcohols, alcohol derivatives, and other oxygenatehave promise as an economical, non-petroleum source for olefinproduction.

Because light olefins are the most sought after products from thecatalytic petroleum cracking and oxygenate conversion processes, acontinuing need exists for new catalysts and/or new ways of making knowncatalysts to increase the yield of light olefin products and/or reducethe yield of unwanted products such as heavy hydrocarbons havingmolecular weights heavier than butane or low-valued by-products likemethane.

Most catalysts that are used in the petroleum cracking and oxygenateconversion processes are molecular-sieve containing catalysts. Amolecular sieve can be zeolitic—zeolites—or non-zeolitic. Typicalexamples of zeolitic molecular sieves are zeolite A, zeolite X zeoliteY, ZSM-5. ZSM-34, erionite, chabazite, and others. A number ofnon-zeolitic molecular sieves, particularly silicoaluminophosphates(SAPO's) have been synthesizcd and investigated as catalysts forconverting oxygenates or cracking heavy hydrocarbons to light olefins.

SAPO's have a three-dimensional microporous crystalline framework of PO₂⁺, AlO₂ ⁻, and SiO₂ tetrahedral units. Because an aluminophosphate(AlPO₄) framework is inherently neutral, the incorporation of siliconinto the AIPO₄ framework by substitution generates add sites andacidity. Controlling the quanity and location of silicon atomsincorporated into an AIPO₄ framework is important in determining thecatalytic properties of a particular SAPO molecular sieve. Properlyadjusted acid strength and acid site density are the keys to a goodpetroleum cracking or oxygenate conversion catalyst.

The catalytic properties of a SAPO catalyst also can be modified afterthe SAPO molecular sieve has been synthesized. This type of“post-synthesis” modification is accomplished by treating the molecularsieve with metallic, semi-metallic or non-metallic materials comprisingnickel, cobalt, manganese, magnesium, barium, strontium, lanthanides,actinides, fluorine, chlorine, chelating agents, and others. Themodifiers may or may not become part of the final composition of themodified catalyst.

SAPO's suitable for converting tho oxygenates to light olefins includeSAPO-17, SAPO-18, SAPO-34 and SAPO-44. These are small-pore molecularsieves with pore diameter smaller than about 5 Angtroms. Small pores arebelieved to favor light olefins production as a result of sievingeffects. For the chabazite-like SAPO-34 and SAPO-44 molecular sieves, itmay be possible to incorporate more silicon atoms into the tetrahedralpositions of the framework to afford greater flexibility in adjustingtheir acidic properties.

A hydrothermal synthesis method for making SAPO-44 was described in USA4,440,871. The materials were aqueous silica sol, aluminum isopropoxide,orthophosphoric acid, and an organic template, cyclohexylamine. Thesynthesis was performed at 200° C. for 52 hours. The SAPO-44 wasobtained as the “major phase” in the product, but the product wasimpure. It contained unidentified materials. A similar method based onthe same starting materials and added hydrofluoric acid (HF) wasreported by U. Lohse et al, in J. Chem. Soc. Faraday Trans. 91, 1155(1995). In the presence of HF, the reaction time was shortened to fivehours at 200° C. It is not clear how pure the SAPO-44 products were.Among the five products reported in the paper, at least one of themcontained SAPO-35 impurity.

Because SAPO-44 can be used as a catalyst for the hydrocarbon crackingand oxygenate conversion processes, it is desirble to produce molecluarsieve catalysts comprising SAP44 from cheaper starting materials and/orunder less demanding reaction conditions. It is preferable to produce amolecular sieve product consisting essentially of SAPO-44. It is alsopreferable to avoid using highly corrosive reactants such ashydrofluoric acid (HF) in the molecular sieve synthesis reactionmixture.

SUMMARY OF THE INVENTION

The present invention provides a method which comprises forming amixture comprising a silicon component; an organic template at a firstmolar ratio of greater than about 1 to an aluminum component; and aphosphorus component at a second molar ratio of less than about 1 to aidaluminum component, and subjecting said mixture to conditions effectoveto produce molecular sieves comprising siliconaluminophosphate 44.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method of making a molecular sievecatalyst comprising silicoaluminophosphate 44 (SAPO-44). preferably insubstantially pure form.

The method generally comprises forming a mixture comprising a siliconcomponent, an aluminum component, a phosphorus component, and atemplate. This mixture then is allowed to go through an optional agingperiod before being subjected to a hydrothermal treatment at an elevatedtemperature. The product formed from the hydrothermal treatment may becalcined further at an elevated temperature. Either before or followingthe optional calcination, the molecular sieve product may be modifiedfurther using an ion-exchange method or other types of modificationssuch as steaming, to produce a molecular sieve comprising SAPO-44,preferably a molecular sieve consisting essentially of pure SAPO-44.

A number of silicon compounds and their mixtures may be used as thesilicon component for the method of the present invention. The siliconcompounds include, but are not limited to silica sol silica gel,colloidal silica, filmed silica, silicic acid, sodium silicate,tetraethyl silicate, tetramethyl silicate, and mixtures thereof. Apreferred silicon component comprises a material selected from the groupconsisting of silica sol, silica gel, colloidal silica, filmed silica,silicie acid, and mixturs thereof The silicon compounds can be purchasedfrom many commercial sources such as Aldrich Chemical Company, du PontCompany, Johnson Matthey Catalog Company, Merck Company and others.

Many aluminum compounds and their mixtures are suitable for use as thealuminum component in the present invention. The aluminum compoundsinclude, but are not necessarily limited to aluminum oxide, boehmite,pseudo boehmite, aluminum hydroxy chloride, aluminum alkoxides such asaluminum tri-isopropoxide, aluminum tri-ethoxide, aluminumtri-n-butoxide and aluminum tri-isobutoxide, and mixtures thereof. Apreferred aluminum component comprises a material selected from thegroup consisting of boehmite and pseudo boehmite. These compounds can bepurchased from many companies such as Aldrich Chemical Company, ReheisCompany, Aluminum Company of America, Vista Company, and others.

The phosphorus compounds suitable for use as the phosphorus componentinclude but are not necessarily limited to orthophosphoric acid,phosphorus acid, trimethyl phosphate, triethyl phosphate, and mixturesthereof. A preferred phosphorus component comprises orthophosphoric acid(H₃PO₄). Another preferred phosphorus component comprises thecommercially available 85 wt % phosphoric acid (in water). Alternately,phosphorus oxides (P₂O₃, P₂O₄, P₂O₅, and POCl₃) may be used, preferablyafter they are dissolved in a suitable solvent such as water. Thesephosphorus compounds can be purchased from companies such as AldrichChemical Company, Merck Company, MTM Research Chemicals, Fluka CheamieAG, and others.

A suitable organic template comprises a material selected from the groupconsisting of organic amines, organic ammonium salts, and mixturesthereof. A preferred organic template comprises cyclohexylamine (CHA).Another preferred template comprises a material selected from the groupconsisting of cyclohexylammonium chloride, cyclohexylammonium bromide,other cyclohexylammonium salts, and mixtures thereof. The organictemplates can be purchased from commercial sources like Aldlich ChemicalCompany, MTM Research Chemicals, and others.

A solvent can be mixed with the organic template before the template isadded to the reaction mixture. Preferably, the organic template iscompletely mixable with, or soluble in, the solvent. Suitable solventsinclude but are not necessarily limited to water, methanol, ethanol,n-propanol, iso-propanol, C₄ alcohols, ethylene glycol, 1,2-propyleneglycol, 1,3-propylene glycol and mixtures thereof. A preferred solventcomprises water.

The aluminum component and the phosphorus are mixed in a suitablesolvent to form a first mixture of uniform composition and texture.Adequate mixing, stirring, or agitation usually is used. To this mixtureis added the silcon component, followed by the organic template.Alternately, the silicon component and the organic template may becombined to form a second mixture of uniform composition and texture.This second mixture is mixed with the first mixture. Other permutationsof how the indivdual components are mixed may be possible so long asfinal mixture with uniform composition and texture is formed.

In order to make a molecular sieve comprising SAPO-44, the molar ratiosof the components in the mixture must be controlled and maintained.Before being subjected to conditions effective to produce the molecularsieve product, the final reaction mixture, excluding any other organicor inorganic moieties or species which may be present is characterizedby a general formula as follows:

T_(a)Si_(w)Al_(x)P_(y)O_(z)·bH₂O

wherein T represents the organic template.

The molar ratio of the organic template to aluminum, a/x, is in therange of from about 1 to about 5, preferably from about 1.2 to about 4.The molar ratio of the template to phosphorus, a/y, is in the range offrom about 1 to about 5. Preferably from about 1.2 to about 4. The molarratio of the template to silicon, a/w, is in the range of from about 2to about 8, preferably from about 2.5 to about 6. The molar ratio ofphosphorus to aluminum, y/x, is in the range from about 1 to about 0.2.The molar ratio of the template to water, a/b is in the range from about0.02 to about 0.2, preferably in the range from about 0.04 to about 0.1.z is the oxygen needed to balance the ionic charges of Si, Al, and Ppresent as expressed in the formula. As long as the molar ratiorequirements of the mixture are satisfied according to the formula shownabove, many different procedures may be used to synthesize a desiredproduct.

It is preferable to maintain the pH value of the final reaction mixturein the range from about 5.5 to about 8.5, preferably from about 6 toabout 7.5. The pH value of a mixture may be adjusted, if desired, byadding an appropriate amount of a base such as ammonia/ammoniumhydroxide to increase the ph, or an appropriate amount of a suitableinorganic or organic acid such as phosphoric acid, HCl, acetic acid,formic acid, CO₂ and others to decrease the pH.

It is preferable to use adequate mixing, blending, stirring, oragitation to provide a uniform composition throughout the mixture. Aconcentration or composition gradient should be minimized because such agradient could result in the formation of different molecular sieveproducts.

Preferably, a constant temperature is maintained during the preparationof the mixture. Mixing of some of the components is notthermodynamically neutral. Cooling or heating may be required to providea constant temperature environment. A suitable temperature forpreparation of a mixture is in the range of from about 10° C. to about90° C., preferably from about 20° C. to about 65° C. Pressure is usuallynot critical for preparing a mixture unless one or more gases are usedto control other reaction parameters, such as pH, temperature, orconcentration.

Once a mixture is prepared, the mixture optionally may be aged for acertain period of time in the range of from about 0 hours to about 200hours before the mixture is subjected to conditions effective to producea desired product comprising SAPO-44. Aging can be accomplished at atemperature in the range of from about 0° C. to about 95° C., preferablyin the range of from about 20° C. to about 65° C., with or withoutagitation/stirring.

After aging, if any, the final reaction mixture is treated underconditions effective to produce a molecular sieve product comprisingSAPO-44, preferably in substantially pure form. The mixture usually isplaced in a metallic autoclave which may be lined with an inert liner toprevent the metal surface of the autoclave from reacting with thereaction mixture. Other pressure vessels made of heavy glass or plasticwalls also may be used as long as the wall material does not react withthe reaction mixture. With or without agitation/stirring, the mixture isheated to a temperature in the range of from about 100° C. to about 270°C., preferably from about 150° C. to about 230° C., for a period of timein the range from about 30 minutes to about 800 hours, preferably in therange from about 5 hours to about 200 hours. The required time perioddepends on the temperature and composition of the mixture.

An autogenic pressure usually is maintained. If preferred, anon-reactive gas such as nitrogen, argon, helium, and mixtures thereofmay be used to provide additional pressure. Other gases also may beused, if desirable. One such gas which may be used to provide pressureand to change the pH value of the mixture is CO₂. CO is another gas thatmay be used unless CO undesirably reacts with the mixture or certaincomponents of the mixture.

After the formation of a SAPO-44 containing product, the product isseparated and recovered by many known techniques, such as filtration,centrifugation, sedimentation, or a combination thereof. The recoveredproduct preferably is dried at a reduced pressure, an elevatedtemperature, or both. A suitable pressure is in the range of from about0.01 kPa to about 150 kPa.

With or without being dried, the recovered product preferably iscalcined to remove the organic templates. The calcination is carried outat a temperature in the range of from about 250° C. to about 800° C.,preferably from about 350° C. to about 650° C. in an oxidizingatmosphere in order to burn off the organic template, preferably in airor an oxygen containing gas. Non-oxidizing atmospheres also may be used,including but not necessarily limited to nitrogen, hydrogen, water(steam) and mixture thereof. Steam also may be used with an oxidizingatmosphere for the calcination. The time period for the calcination isin the range of from about 30 minutes to about 72 hours, preferably fromabout 2 hours to about 48 hours.

Using the methods known in the art, the SAPO-44 molecular sieve productscan be further ion-exchanged into an essentially complete hydrogen formwith very low level of residual metal ions. Controlled ion-exchange alsocan be carried out to make a partial hydrogen form, or a fullyion-exchanged form of a SAPO-44 molecular sieve.

Catalysts made according to the present invention can be used to convertoxygenates to olefins, or to convert hydrocarbons to lower molecularweight products, particularly to light olefins (ethylene, propylene,butenes and mixtures thereof).

Oxygenates can be converted to olefins by contacting an oxygenate feedwith a catalyst comprising SAPO-44 under conditions effective to produceolefins, preferably light olefins such as ethylene, propylene, butenes,and mixtures thereof.

Oxygenates suitable for use in the feed include, but are not necessarilylimited to aliphatic alcohols, ethers, carbonyl compounds (aldehydes,ketones, carboxylic acids, esters, carbonates and the like), alkylhalides, alkyl amines, and mixtures thereof. Preferred oxygenates aremethanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol,dimethyl ether, methylethyl ether, diethyl ether, dimethyl carbonate,and mixtures thereof.

Effective conditions for oxygenate conversions are known in the art, andinclude, but are not necessarily limited to: a temperature in the rangefrom about 200° C. to about 800° C.; a pressure in the range of fromabout 1 kPa to about 2 Mpa; a Weight Hourly Space Velocity (WHSV) in therange of from about 0.01 to about 10,000 h⁻¹. Because the feed maycontain diluents and the catalyst may contain filler and/or bindermaterials, WHSV is calculated on the weight of the oxygenate feed itselfand the weight of the molecular sieve component in the catalyst.Diluents can be mixed with the oxygenates as feed. The amounts ofdiluent used are in the range of from about 0 wt % to about 95 wt % ofthe total feed. Suitable diluents include but are not necessarilylimited to water (steam), CO₂, hydrogen, nitrogen, argon, and mixturesthereof.

The oxygenate feed is contacted with the catalyst in a conversionreactor under effective conditions for conversion. A suitable conversionreactor is a fixed bed reactor, a moving bed reactor, a fluidized bedreactor, or another similar type of reactor. The products and anyunreacted feedback then are separated from the catalyst, and theproducts are purified. Unreacted feedstock may be recycled back to theconversion reactor or otherwise disposed. If the catalyst isdeactivated, it is regenerated. Regeneration can be carried out in theconversion reactor itself or in a separate regeneration reactor.Regeneration usually is carried out at an elevated temperature, in therange of from about 350° C. to about 95° C., and in the presence of anoxygen containing atmosphere. Sometimes treating a deactivated catalystwith hydrogen at elevated temperatures also is effective to regeneratethe catalytic performance of the oxygenate conversion catalyst.

Catalysts of the present invention also can be used for conversion ofrelatively high molecular weight hydrocarbons to hydrocarbons havinglower molecular weight Suitable hydrocarbon feedstocks include, but arenot necessarily limited to naphtha and similar hydrocarbons. Thefeedstocks preferably comprise mostly non-aromatic compounds with atleast five carbon atoms. Preferred products comprise light olefins(ethylene, propylene, butenes, and mixtures thereof.

Typical reaction conditions for the hydrocarbon conversions are known inthe art, and include, but are not necessarily limited to: a temperaturein the range of from about 250 to about 900° C., a pressure in the rangeof from bout 1 kPa to about 2 Mpa; a weight hourly space velocity (WHSV)in the range of from about 0.01 to about 10,000 h⁻¹. Because the feedmay contain diluents and the catalyst may contain filler and/or bindermaterials, WHSV is calculated on the weight of the hydrocarbon feeditself and the weight of the molecular sieve component in the catalyst.Diluents such as water (steam), CO₂, hydrogen, nitrogen, and others canbe mixed with the feedstocks, The amounts of diluents used are in therange of from about 0 wet to about 95 wt % of the total feed.

The hydrocarbon feed is contacted with the catalyst in a conversionreactor under effective conditions for conversion. A suitable conversionreactor is a fixed bed reactor, a moving bed reactor, a fidized bedreactor, or other similar types of reactor. The products and anyunreacted feedstock then are separated from the catalyst, and theproducts are purified. Unreacted feedstock may be recycled back to theconversion reactor or otherwise disposed. If the catalyst isdeactivated, it is regenerated. Regeneration can be carried out in theconversion reactor or in a separate regeneration reactor. Regenerationusually is carried out at an elevated temperature in the range of fromabout 350° C. to about 950° C., and in the presence of oxygen. Sometimestreating a deactivated catalyst with hydrogen at elevated temperaturesalso is effective to regenerate the catalytic performance of thehydrocarbon conversion catalyst.

The invention will be better understood with reference to the followingexamples, which illustrate, but do not limit the invention, which issolely defined by the claims.

EXAMPLE I

A reaction mixture was prepared by mixing 11.53 g of 85 wt %orthophosphoric acid and 15.5 g of water. To this mixture was added 6.87g of boehmite (74.2 wt % alumina and 25.8 wt % water) with adequatestirring to make the mixture uniform. 6.9 grams of silica gel (26 wt %SiO₂, 74wt % H₂O) were added and the mixture was stirred to becomehomogeneous. Finally, 17.1 grams of cyclohaxylamine (CHA) (100%) and11.9 grams of water were added to this mixture with stirring to form ahomogeneous mixture. The composition of the final reaction mixture inmolar oxide ratios was 3 CHA:Al₂O₃: P₂O₅: 0.6 SiO₂:40 H₂O. This reactionmixture was sealed in a 100 ml stainless steel vessel and heated in anoven at 200° C. at autogeic pressure for 72 hours. The reaction mixturewas then filtered, washed with distilled water, and dried at 110° C. torecover a solid product, “as-sythesized” SAPO-44. This “as-synthesized”SAPO-44 was calcined by heating to 550° C. over two hours in air andthen maintained at 500° C. for another three hours. The Al₂O₃: P₂: O₅:SiO₂ molar ratio in the product was about: 1:0.74:0.92. X-raydiffraction (XRD) showed that the product was substantially pureSAPO-44. No by-products were identified by XRD. Nuclear magneticreaonance (NMR) of sliicon-29 showed that silicon distribution forSi(4Al):Si(3Al):Si(2Al):Si(1Al):Si(0Al) in the product was (in atomic %)61.0:23.7:5.5:4.2:5.6. Si(4Al) means that the silicon atom is surroundby four Al—O— groups; Si(3Al), three; Si(2Al), two; Si(1Al), one; andSi(0Al), zero such Al—O— groups.

EXAMPLE II

Procedures similar to EXAMPLE I were repeated except that the compositonof the final reaction mixture in molar oxide ratios was 3 CHA:Al₂O₃:P₂O₅: SiO₂: 40 H₂O. The Al₂O₃:P₂O₅: SiO₂ molar ratio in the SAPO-44molecular sieve product was about: 1: 0.77: 0.85. X-ray diffractionQXRD) showed that the product was substantially pure SAP-044. Noby-products were identified by XRD. Silicon-29 NMR showed that silicondistribution for Si(4Al):Si(3Al):Si(2Al):Si(1Al):Si(0Al) in the productwas (in atomic %) 45.3:23.9:11.5:9.9:9.8.

EXAMPLE III

Procedures similar to EXAMPLE I were repeated except that thecomposition of the final reaction mixture in molar oxide ratios was 2CHA : Al₂O₃:P₂O₅: SiO₂: 0.6 SiO₂: 80 H₂O. The Al₂O₃:P₂O₅: SiO₂ molarratio in the SAPO-44 molecular sieve product was about: 1: 0.68: 1.41.X-ray diffraction (XRD) showed that the product was substantially pureSAPO-44. No by-products were identified by XRD. Silicon NMR showed thatsilicon distribution for Si(4Al):Si(3Al):Si(2Al):Si(1Al):Si(0Al) in theproduct was (in atomic %): 30.9:23.5:15.9:15.6:13.7.

EXAMPLE IV

The catalysts prepared in EXAMPLES, I, II, and III were tested for theirability to convert methanol to olefins. The catalysts were pelletizedand crushed to 20-40 mesh in size. 1.28 grams of each catalyst weretested separately in a tubular reactor. Prior to use, the catalysts weretreated at 500° C. in a flowing nitrogen stream, 60 ml/min, for onehour. The methanol conversion reactions were carried out at a 2 h⁻¹weight hourly space velocity (WHSV) of methanol feed in a nitrogencarrier gas at 60 ml/min. The WHSV was measured for methanol only,excluding nitrogen. The data reported below were obtained after thereaction was on-stream for two minutes. The products were analyzed by astandard gas chromatographic methods. The results are shown below:

EXAMPLE EXAMPLE EXAMPLE Catalyst I II III Methanol Conversion (wt %) 100100 100 Selectivity (wt %) CH₄ 1.2 1.1 1.7 C₂H₄ 39.6 31.4 26.0 C₂H₆ 0.51.0 3.1 C₃H₆ 39.2 34.9 32.7 C₃H₈ 5.4 12.2 21.3 C₄H₈ 11.9 12.9 12.9 C₄H₁₀2.2 2.4 2.4 C₅ ⁼ 0 4.1 0 C₅ ⁺ 0 0.1 0

These results indicate that molecular sieves comprising substantiallypure SAPO-44 could be prepared according to the method of the presentinvention. The molecular sieves are capable of converting methanol tolight olefins in high selectivities.

Persons of ordinary skill in the art will recognize that manymodifications may be made to the present invention without departingfrom the spirit and scope of the present invention. The embodimentsdescribed herein are meant to be illustrative only and should not betaken as limiting the invention, which is defined in the followingclaims.

We claim:
 1. A SAPO-44 molecular sieve, wherein said SAPO-44 comprises30.9 to 61.0 percent Si(4Al) species.
 2. A SAPO-44 molecular sieve asclaimed in claim 1, wherein said SAPO-44 contains 45.3 to 61.0 percentSi(4Al) species.
 3. A SAPO-44 molecular sieve which is made by a methodcomprising: forming a mixture comprising, a silicon component, analuminum component, an organic template at a ratio of organic templateto aluminum of at least 1, and a phosphorus component; and subjectingsaid mixture to conditions effective to produce said SAPO-44 , whereinthe SAPO-44 contains 30.9 to 61.0 percent Si(4Al) species.
 4. A SAPO-44molecular sieve according to claim 3, wherein said SAPO-44 contains 45.3to 61.0 percent Si(4Al) species.
 5. A SAPO-44 molecular sieve made by amethod comprising: forming a mixture comprising, a silicon component, analuminum component, a phosphorus component, and an organic template,said mixture having the formula T_(a)Si_(w)Al_(x)P_(y)O_(z)·b H₂O,excluding other species present in said mixture, wherein T representsthe organic template, a/w is from about 2 to about 8, a/x is from about1 to about 5, a/y is from about 1 to about 5, y/x is from about 1 toabout 0.2, and a/b is from about 0.02 to about 0.2; and subjecting saidmixture to conditions effective to produce said SAPO-44, wherein saidSAPO-44 contains 30.9 to 61.0 percent Si(4Al) species.
 6. A SAPO-44molecular sieve according to claim 5, wherein said SAPO-44 contains 45.3to 61.0 percent Si(4Al) species.
 7. A SAPO-44 molecular sievecomposition made by a method comprising: mixing boehmite with an aqueousorthophosphoric acid solution under first condition effective to form afirst product; adding a silica gel to said first product under secondconditions effective to form a second product; adding a mixturecomprising cyclohexylamine and water to said second product under thirdconditions effective to form a third product wherein said third productexhibits a pH from about 5.5 to about 8.5 and comprises a compound ofthe formula T_(a)Si_(w)Al_(x)P_(y)O_(z)·b H₂O, wherein T representscyclohexylamine, a/w is from about 2 to about 8, a/x is from about 1 toabout 5, a/y is from about 1 to about 5, y/x is from about 1 to about0.2, and a/b is from about 0.02 to about 0.2; subjecting said thirdproduct to a temperature in the range of from about 100° C. to about270° C. for a period of time sufficient to form a solid material; dryingsaid solid material at a temperature from about 25° C. to about 120° C.and at a pressure from about 0.01 kPa to about 150 kPa to form a driedsolid material; and calcining said dried solid material to form saidSAPO-44 molecular sieve composition, wherein said SAPO-44 has 30.9 to61.0 percent Si(4Al) species.
 8. A SAPO-44 molecular sieve compositionas claimed in claim 7, wherein said SAPO-44 contains 45.3 to 61.0percent Si(4Al) species.
 9. A SAPO-44 molecular sieve made from areaction mixture having the formula T_(a)Si_(w)Al_(x)P_(y)O_(z)·b H₂O,wherein T represents an organic template, a/w is from about 2 to about8, a/x is from about 1 to about 5, a/y is from about 1 to about 5, y/xis from about 1 to about 0.2, and a/b is from about 0.02 to about 0.2,wherein said SAPO-44 contains 30.9 to 61.0 percent Si(4Al) species. 10.A SAPO-44 molecular sieve as claimed in claim 9, wherein said SAPO-44contains 45.3 to 61.0 percent Si(4Al) species.